You could be mistaken in the slang usage of crazy. It is generally used adjectivally to a positive/ emphasizing effect, not negatively as in the example. "This TV show is crazy addictive!" would be fine in slang. On the other hand, "not as crazy addictive" contradicts the emphasis.
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KrisFeb 10 '13 at 11:50

I think younger speakers increasingly use crazy as a general-purpose intensifier equivalent to very, so they don't necessarily see anything ungrammatical in OP's usage. By contrast, you'll very rarely hear anything referred to as ?insane addictive.

Ah yes, Google Books, that fine resource not yet available in my country. When region coding comes to literature. Let's make it unavailable to all US Immigrants from other countries. You're not being consistent and thorough, Google.
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Henrik ErlandssonApr 21 '13 at 16:41

@Henrik: That's a bummer. Can you maybe get around it by going through a proxy server? (just don't ask me how you do that, 'cos I haven't got a clue! :)
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FumbleFingersApr 21 '13 at 20:41

Crazily addictive would be the more correct form, adjectives are modified by adverbs, not by other adjectives.

You could use crazy addictive very informally, where it would be interpreted as a deliberate bending of the rules to produce a slangy-sounding phrase. If you aren't confident you know exactly why it's bending the rules though, you're probably better of not using it. The trick is to sound like someone who knows it's not really allowed, but did it anyway, rather than someone who just doesn't know.

"Crazy addictive" is fine in the US and used all the time. But it is slang. So if your register is informal, it's fine. However, the best way to express your feeling is by just using the word "addictive". " This TV show is not as addictive as that one."